Novel Pseudomonas aeruginosa Strains Co-Harbouring bla(NDM-1) Metallo β-Lactamase and mcr-1 Isolated from Immunocompromised Paediatric Patients

BACKGROUND: The rising resistance to carbapenems in Gram-negative bacteria worldwide poses a major clinical and public health risk. This study aimed to characterise carbapenem- and colistin-resistance genes, bla(NDM-1) and mcr-1 located on IncX4 plasmid in MDR Pseudomonas aeruginosa, isolated from paediatric patients undergoing chemotherapy as a result of leukaemia. METHODS: In this study, six carbapenem-resistant strains of P. aeruginosa were isolated from two paediatric patients under chemotherapy treatment (1.8 years old female and 2.1 years male) from the Shenzhen Hospital, China, in the year 2019. Isolates were screened for conventional antibiotics such as tobramycin, cefepime, imipenem, and ciprofloxacin in additional colistin by using the broth dilution method. Furthermore, resistance determinants: mcr-1, bla(NDM-1,) bla(KPC-1,) and bla(GES) were screened using PCR and sequencing followed by multi-locus sequence typing. The horizontal gene transfer and location of mcr-1 and bla(NDM-1) were determined by a liquid mating assay. In addition, Incompatibility type (Inc), PCR-based replicon type, and subgroup (MOB) of plasmid were studied. RESULTS: The screening for conventional antibiotics isolates showed 100% resistance to all the tested antibiotics except tobramycin. All isolates harboured carbapenemase encoding bla(NDM-1), of which three also had mcr-1 located on a single IncX4 transferable plasmid. MLST typing revealed that four strains had a novel (new) STs type, while two belonged to ST1966. CONCLUSION: This study identified for the first time colistin- and carbapenem-resistant MDR P. aeruginosa in paediatric patients with leukaemia in Shenzhen, China. It highlights the need for continuous surveillance in high-risk clones of MDR P. aeruginosa. Prudent use of antibiotics based on local antimicrobial susceptibility and clinical characteristics can help in reducing mortality in immunocompromised patients.